Measurement of Suspended Sediment Transport Processes in Shallow Water off the Holderness Coast, UK

A new benthic tripod system has been developed to study the processes responsible for suspended sediment movement in the shallow water (10–20 m depth) off the Holderness coast, N.E. England. About a month of data from a summer period and a winter period are described. The suspended sediment concentration (SSC) is found to vary due to the advection of spatial gradients of SSC by the tidal flows and to the resuspension of sediment from the seabed. Alongshore advection is identified through a strong negative correlation between SSC and salinity, associated with the movement of low salinity, high turbidity water associated with the Humber plume to the south. Resuspension occurs predominantly during storms, when the influence of waves increases the friction velocity at the seabed (estimated from the measured turbulence spectra) above a threshold value. In winter the threshold friction velocity is found to be approximately 0.028 ms−1, consistent with a partially consolidated fine sediment seabed; in the summer period a somewhat lower threshold may be the result of a less consolidated layer of fine sediment depositing between the mild summer storms. The decay of the elevated SSC values after a storm is consistent with a sediment settling velocity in the range (1.8–2.8) × 10−4 ms−1, a value associated with fine silt or floculated clay particles.